Question

I’m having tough time figure out how to display object’s properties in ArrayList using EL expression.

Many tutorial outside shows simple example like:

List<String> test = new ArrayList<String>();
request.setAttribute("test", test);
test.add("moo");

And it works fine.

<p>${test[0]}</p>

When the ArrayList contains actual object with properties, the value does not show up.
The code below gets the query result and store into Data Transfer Object “DTOTopics” then
I add the object into the ArrayList.

    List<DTOTopics> list = new ArrayList<DTOTopics>();
    request.setAttribute("recentTopics", list);
    list = factory.getDAOTopics().findByLimit(5);

HTML

Each element in ArrayList is the object DTOTopics, so I tried to access to one of its properties “title” and nothing shows up on the page.

<h1>${recentTopics[0].title}</h1> //why this doesn't work???

Servlet

public class ShowRecentTopicsAction implements Action {

 @Override
 public String execute(HttpServletRequest request, HttpServletResponse response) throws Exception {

  DAOFactory factory = null;
  List<DTOTopics> list = new ArrayList<DTOTopics>();
  request.setAttribute("recentTopics", list);

  try {
   factory = DAOFactory.getInstance();
   list = factory.getDAOTopics().findByLimit(5);
  } 
  catch (DAOConfigurationException e) {
   Logger.log(e.getMessage() + " DAOConfEx, PostRegisterServlet.java.", e.getCause().toString());
  }
  catch (DAOException e) {
   Logger.log(e.getMessage()+ " DAOEx, PostRegisterServlet.java", e.getCause().toString());
  }

  System.out.println("getRecentTopics() list = " + list);//just check if list returns null

            //for testing
  DTOTopics t = list.get(0);
  System.out.println("TEST:::" + t.getTitle()); //ok

            //these test works fine too
  List<String> test = new ArrayList<String>();
  request.setAttribute("test", test);
  test.add("moo");
  Map<String, String> map = new HashMap<String, String>();
  request.setAttribute("mmm", map);
  map.put("this", "that");

  return "bulletinboard";
 }

}

Answer 1

Here,

List<DTOTopics> list = new ArrayList<DTOTopics>();
request.setAttribute("recentTopics", list);

you’re putting an empty arraylist in the request scope.

And then,

try {
    factory = DAOFactory.getInstance();
    list = factory.getDAOTopics().findByLimit(5);

you’re reassigning the list reference with a new arraylist (instead of filling the original arraylist using add() or addAll() method). The one in the request scope still refers to the original empty arraylist!

Move request.setAttribute("recentTopics", list); to after you’ve obtained the list from the DAO and it should work. Your EL is perfectly fine.